Module 10: Cardiac Physiology

Pulmonary Circuit

Right side of the heart that receives oxygen-poor blood from tissues.

Systemic Circuit

Left side of the heart that receives oxygenated blood from lungs.

Pericardium

Double-walled sac that surrounds the heart.

Pericarditis

Inflammation of the pericardium, leading to friction rub.

Myocardium

Thick middle layer of the heart wall composed of cardiac muscle.

Endocardium

Inner lining of the heart chambers that is continuous with blood vessels.

Atrioventricular Valves

Valves connecting the atria and ventricles that prevent backflow during contraction.

Semilunar Valves

Valves that prevent backflow into ventricles after blood is ejected.

Preload

Stretch dependent factor that impacts force of contraction due to venous return

Contractility

Stretch independent force of contraction due to extrinsic factors

Afterload

The pressure the ventricles must overcome to eject blood

Heart Rate (HR)

Number of beats of the heart per minute.

Stroke Volume (SV)

Volume of blood pumped out by one ventricle with each beat

Cardiac Output (CO)

Volume of blood pumped by each ventricle in one minute; CO = HR x SV.

Electrocardiogram (ECG or EKG)

A composite of all action potentials generated by nodal and contractile cells at a given time

Pacemaker (autorhythmic) cells

Have unstable resting membrane potentials due to opening of slow Na+ channels

Arrhythmias

Irregular heart rhythms.

Cardiac Cycle

The sequence of events in one heartbeat, including contraction and relaxation.

Dicrotic Notch

Brief rise in aortic pressure that occurs when SL valves close.

Heart Murmurs

Abnormal heart sounds usually indicative of valve dysfunction.

Coronary Circulation

Functional blood supply to the heart muscle itself.

Right Atrium

Receives blood returning from systemic circuit

Right Ventricle

Pumps to lungs to get rid of CO2, pick up O2

Left Atrium

Receives blood returning from pulmonary circuit

Left Ventricle

Pumps blood to body tissues

Epicardium

Visceral layer of serous pericardium

Interatrial septum

Separates atria

Fossa ovalis

Remnant of foramen ovale of fetal heart

Interventricular septum

Separates ventricles

Heart Valves

Ensure unidirectional blood flow through heart. Open and close in response to pressure changes. Contraction/relaxation

Two semilunar (SL) valves

Prevent backflow into ventricles when ventricles relax

Two artrioventricular (AV) valves

Prevent backflow into atria when ventricles contract

Stenosis

A narrowing of an open heart valve

Regurgitation/Inefficiency

Back flow of blood through a closed heart valve

Coronary Circulation

Functional blood supply to heart muscle itself, arterial supply varies among individuals, contains many anastomosis (junctions)

Agina pictorial

Thoracic pain caused by fleeting deficiency in blood delivery to myoardium

Myocardial infarction (heart attack)

Prolonged coronary blockage, areas of cell death repaired with non-contractile scar tissue

Autorhythmic cells

No RMP exists in these cells, Ca2+ is responsible for the part of the depolarization phase

Funny channels

Create the pacemaker potential allowing Na+ to leak into the cell when resting which slowly depolarizes the cell. Permeable to K+ and Na+.

Sinaotrail (SA) node

Pacemaker of heart in right atrial wall, depolarizes faster than rest of myocardium, generates impulses about 75x per minute, inherent rate of 100x /minute tempered by extrinsic factors. Impulses spread. Across atria and to AV node

Atrioventricular (AV) node

Inferior interatrial septum, delays impulses ~0.1 sec, bc fibers are smaller diameter, have fewer gap junctions, allows atrial contraction prior to ventricular contraction, inherent rate of 50x/minute in absence of SA node input

Atrioventricular (AV) bundle (bundle of His)

In superior interventricular septum, inherent rate of 40x/minute in absence of SA/AV node input, only electrical connection between atria and ventricles, atria and ventricles not connected via gap junctions

Right and left bundle branches

Two pathways in interventricular septum, carry impulses toward apex of heart

Subendocardial conducting network

Complete pathway through interventricular septum into apex and ventricular walls, more elaborate on left side of heart AV bundle and subendocardial conducting network depolarize 30/min in absence of AV node input

Fibrillation

Rapid, irregular contractions; useless for pumping blood. Circulation ceases → brain death

Cardioacceleratory center

Sympathetic → affects SA, AV nodes, heart muscle, coronary arteries. Threshold for pacemaker potential reached more quickly

Cardioinhibitory center

Parasympathetic → inhibits SA and AV nodes via vagus nerves. Threshold is reached slower

P wave

Depolarization of SA node → arterial depolarization

QRS complex

Ventricular depolarization and atrial repolarization

T wave

Ventricular repolarization

Heart blocks

Issues with the AV nodes

Atrial fibrillation

SA node not controlling rates → AV node takes over

Ventricular fibrillation

No pacemaker is in control. Electric shock resets the intrinsic rates

Systole

Contraction

Diastole

Relaxation

Ventricular filling

Takes place in mid-to-late diastole, AV valves are open; pressure low, 80% of blood passively flows into ventricles, atrial systole occurs, delivering remaining 20%

End diastole volume (EDV)

Volume of blood in each ventricle at end of ventricular diastole

Ventricular systole

Atria relax; ventricles begin to contract. Rising ventricular pressure → closing of AV valves. Isovolumetric contraction phase (all valves are closed). In ejection phase, ventricular pressure exceeds pressure in large arteries, forcing SL valves open

End systolic volume (ESV)

Volume of blood remainint in each ventricle after systole

Isovolumetric relaxation

Early diastole. Ventricles relax, atria relaxed and filling. Backflow of blood in aorta and pulmonary trunk closes SL valves. When atrial pressure exceeds that in ventricles → AV valves open; cycle begins again

Cardiac output

Volume of blood pumped by each ventricle in one minute. CO = HR x SV. Normal: 5.25 L/min